1. Field of the Invention
The present invention relates to rotary piston engines, and more particularly to rotor housings for rotary piston engines. More specifically, the present invention pertains to rotor housings having improved inner wall surfaces.
2. Description of the Prior Art
In rotary piston engines, the inner wall surface of the rotor housing and the apex seals on the rotor which slidably moves on the inner wall surface of the rotor housing are subjected to mechanical loads due to vibrations, impact loads and frictions, as well as thermal loads due to the combustion in the engine. Usually, the inner wall surface of the rotor housing is applied with hard chromium plating layer but, due to the aforementioned mechanical loads and the thermal loads to which the rotor housing is subjected, there are very often produced in the chromium plating layer on the rotor housing uneven wear such as chatter marks and scratches.
In order to avoid the problems, proposals have been made to appropriately determine the hardness of the apex seal with respect to the hardness of the chromium plating layer on the rotor housing, or to provide the chromium plating layer with porous structure of for example pin-point type or channel-type so that lubricant oil can be retained in the pores. Such solutions have already been known in the art of reciprocating piston engines. For example, Japanese patent publication No. 41-18604 teaches to provide a cylinder liner with a plating layer of a corrosion resistant Cr-Mo alloy containing 1 to 5% of Mo, the layer being covered a porous chromium plating layer which is superior to the Cr-Mo alloy layer in respect of machining property and the intimacy to the piston ring. The proposal is based on the recognition of the fact that the Cr-Mo alloy has a high hardness and therefore shows a superior wear resistant property but it does not have a good machining property, and is aimed to provide a satisfactory machining property by the porous chromium layer. It should however be noted that the proposed structure has problems in that the chromium plating layer is destroyed after initial operations of the engine so that there will be a loss in the lubrication property.
Further problems are encountered in recent supercharged high power rotary piston engines in that the lubricating oil film on the inner wall of the rotor housing is broken due to a high temperature in the working chambers and the high combustion pressure. Therefore, the inner wall surfaces of these engines are subjected to very serious conditions so that conventional technologies are not sufficient to meet the requirements in these high power engines.
In order to solve the problems, the quantity of the lubricating oil supplied to the inner wall surface of the rotor housing may be increased to thereby provide a satisfactory lubrication. It should however be noted that the solution is not recommendable because there will be an increase in the oil consumption and also an adverse effect on the pollutant emissions in the engine exhaust gas. It is therefore highly desirable to provide an effective means to solve the aforementioned problems.